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Ascidian gene-expression profiles

DOI: 10.1186/gb-2002-3-10-reviews1030

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Molecular analysis of development has traditionally involved studies of one or a few genes at a time. This approach has revealed powerful regulatory genes, which have become the foundation for understanding pattern formation during metazoan development. But with one notable exception [1], the detailed genetic networks in which developmental genes function have remained elusive. Researchers working on the development of several model organisms are now breaking the single-gene tradition by using expressed sequence tag (EST) analysis to identify random cDNA clones from libraries derived from different stages and tissue types, and high-throughput in situ hybridization to categorize the corresponding mRNAs by their expression domains. In concert with antisense-mediated inhibition of gene expression and other molecular tools of developmental biology, EST analysis and other methods of gene-expression profiling can shed new light on the genetic circuitry underlying developmental processes. Here, I review recent gene expression-profile analysis in ascidians and the promise of this approach for studying developmental gene networks.The ascidians are members of the tunicate (or urochordate) branch of the chordate tree and have been popular models in embryology and evolutionary biology for more than a century [2,3]. Their chordate features include a dorsal nervous system and a notochord in the larval phase of the life cycle, and pharyngeal gill slits in the adult phase (Figure 1). The favorable attributes of ascidians for traditional developmental biology include rapid embryogenesis, stereotypic cleavage divisions of the zygote and early embryo, well-documented cell lineages, low embryonic cell numbers, few larval tissue types, and a simplified larval body plan. Ascidian development starts with the localization of determinants in the egg; inductive signaling between different cells then takes place during the cleavage period, followed by simple morphogenetic movements that lead


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